A method of manufacturing a thermal head in the related art will now be described with reference to a thermal head disclosed in JP-A-05-069575, for example. As shown in FIG. 7, a plurality of heating elements 22 are arranged on a head substrate 21 in a longitudinal direction (a row direction of printing) of the head substrate 21.
A method of manufacturing the thermal head includes forming a plurality of heating elements 22 in the longitudinal direction by using a photolithographic technique. In this case, a central portion of the plurality of heating elements 22 is bent downward from both ends of the heating elements 22 by a warpage amount of ‘t’. The warpage amount of ‘t’ corresponds to the warpage amount of a platen roller 23, which will be described later, occurring at the time of printing.
The head substrate 21 is provided on a head mounting member (not shown) made of, for example, aluminum having an excellent heat-radiating property.
The platen roller 23 presses an ink ribbon and record paper (not shown). As shown in FIG. 8, the platen roller 23 is provided on the heating elements 22 which are bent. The platen roller 23 includes a friction member 23a, such as a rubber cylinder, and a slender mandrel 23b, which is inserted into the center of rotation of the friction member 23a and is rotatably supported by a printer (not shown).
While the platen roller 23 presses the record paper and ink ribbon on the heating elements 22 at the time of printing, the central portion of the platen roller 23 rotating counterclockwise is bent to the direction of arrow C by friction between the record paper and the friction member 23a as shown in FIG. 8.
Since the thermal head in the related art includes the heating elements 22 of the head substrate 21 which are bent by a warpage amount of ‘t’, the platen roller 23 may uniformly press the ink ribbon and record paper on the heating elements 22 by pressure even though the platen roller 23 is bent to the direction of arrow C at the time of printing.
However, since the thermal head in the related art includes a plurality of heating elements 22 which are bent by a warpage amount of ‘t’, a curved line is printed along the heating elements 22 when the heating elements 22 emit heat at the same time. Accordingly, the heat emission of the heating elements 22 is controlled to correspond to the curve of the heating elements 22 by a driver IC (not shown) in order to print a straight line. However, it is very difficult to control the heat emission by means of the driver IC.
Further, when the head substrate 21 of the thermal head is narrow in width ‘A’, the head substrate 21 is partially thermally expanded by the heat of the heating elements 22 which occurs at the time of printing, such that the central portion of the head substrate 21 warps to the direction of arrow B (called ‘banana warpage’).
As a result, even though a plurality of heating elements 22 is bent by a warpage amount of ‘t’ before emitting heat, the head substrate 21 may be bent to a direction opposite to that of the heating elements 22 when the heating elements 22 emit heat at the time of printing, and the platen roller 22 may not be uniformly pressured to the heating elements 22.